1. Field of the Invention
The invention pertains to a head for the measurement of magnetic fields using the effect of the magnetic field on the polarization of light, a measuring head wherein the light source, the element sensitive to the magnetic field, the detector, any optical transmission element between the said elements as well as the electronics system for the processing of the detected signal are made monolithically on one and the same substrate. Depending on the embodiment, this measuring head can be applied to the measurement of magnetic fields or to the measurement of the gradient vector of magnetic fields.
The invention also pertains to a method of manufacture which can be used to make a head of this type.
2. Brief Description of the Prior Art
Prior art devices include measuring heads for magnetic field measuring instruments which use the influence of a magnetic field on the polarization of light to measure this magnetic field.
Thus, the French patent No. 76 18600 filed on 18th June 1976 and published under No. 2 355 299 on 13th Jan. 1978 describes an apparatus comprising:
A light source emitting a plane-polarized light beam;
A flat, thin layer of a magnetic material which is placed into the magnetic field to be measured and makes it possible to propagate the light beam in a guided manner;
A detector which receives the light beam after it has crossed the thin layer of magnetic material and which measures the light intensity of the beam.
The light beam is propagated in the thin layer in a single mode, TM for example. Because of the Faraday effect, the magnetic field causes the mode of propagation to be converted into the TE mode in a percentage that varies according to the value of the magnetic field. A rotation of the plane of polarization of the light is obtained and can be measured by the detector.
In another device of the prior art, described in the French patent No. 79 30721 filed on 14th Dec. 1979 and published under No 2 471 608 on 19th June 1981, and element propagating the light beam, placed in the magnetic field to be measured, is a thick layer of magnetic material used for a multimode light transmission. As above, because of the Faraday effect, the light beam experiences a rotation of its plane of polarization in the presence of a magnetic field. The rotation of this plane of polarization is brought about by means of crossed polarizers.
An arrangement of this type has been applied to the making of a device for measuring magnetic field gradients in the French patent application No. 83 11073 filed on 4th July 1983. In this device, two magnetic field measuring cells are placed on a single light beam. In this way, it is possible to measure a magnetic field gradient along a direction determined by the direction of the light beam. This patent also describes a system which can be used to measure the Faraday effect by means of a zero method using auxiliary windings that transmit a magnetic field cancelling the field to be measured.
However, the devices of the prior art are not made monolithically, and their design does not provide for an embodiment of this type. Consequently they take the shape of an association of hybrid components, a fact that raises two essential problems:
The performance characteristics of the components are difficult to reproduce;
The implanting of the components into one another calls for many precautionary measures.
The magnetic field measuring head of the invention and the method for making the said measuring head remove these disadvantages.
3. Summary of the Invention
Thus, an object of the invention is a magnetic field measuring head comprising:
a light source emitting a first beam of plane-polarized light;
a first flat layer of magnetic material placed in the path of the said light beam and placed into a magnetic field to be measured, the effect of which is to cause the rotation of the plane of polarization of the light;
first means to measure the rotation of the plane of polarization of the light, the said means being placed in the path of the said beam after it has crossed the layer of magnetic material;
a measuring head wherein the light sources and the layer of magnetic material are integrated into one and the same substrate and wherein they each possess a lattice parameter which is equal to or is a multiple or sub-multiple of the lattice constant of the substrate (1), the light source being coupled to the layer of magnetic material by a first light guide which is integrated into the said substrate and is insensitive to the magnetic field.
Another object of the invention is a method for making a measuring head of this type, a method comprising the following various, successive stages:
(a) A first stage for the machining, in a substrate, of a first light guide having a first end and a second end;
(b) A second stage for the masking of the said light guide made in this way;
(c) A third stage for the growth of a first layer of a ferrimagnetic material set at the second end of the said light guide;
(d) A fourth stage for the growth, on the substrate in a zone attached to the first end of the light guide, of an emitting diode made of a material having a lattice parameter which is substantially equal to or is a multiple or sub-multiple of the lattice constant of the substrate;
(e) A fifth stage for the growth, on the substrate in a zone attached to the first layer of ferrimagnetic material, of a receiving diode made of a material having a lattice parameter which is substantially equal to or is a multiple or sub-multiple of the lattice constant of the substrate;
(f) A sixth stage for making the processing circuits.